Electrical and thermal insulation for a combustion system

ABSTRACT

An electrically enhanced combustor includes bilayer insulation. A thermal insulator protects an electrical insulator from high temperatures that could cause the electrical insulator to become at least somewhat electrically conductive.

CROSS REFERENCE TO RELATED APPLICATIONS

The present application is a U.S. Continuation application which claims priority benefit under 35 U.S.C. §120 (pre-AIA) of co-pending International Patent Application No. PCT/US2014/058853, entitled “ELECTRICAL AND THERMAL INSULATION FOR A COMBUSTION SYSTEM,” filed Oct. 2, 2014 (docket number 2651-192-04); which application claims priority benefit from U.S. Provisional Patent Application No. 61/885,809, entitled “ELECTRICAL AND THERMAL INSULATION FOR A COMBUSTION SYSTEM,” filed Oct. 2, 2013 (docket number 2651-192-02), co-pending at the date of filing; each of which, to the extent not inconsistent with the disclosure herein, is incorporated herein by reference.

SUMMARY

One embodiment is a combustor wall that includes a conductive wall defining an exterior surface, a thermal insulator defining an interior surface configured to lie adjacent to a combustion volume configured to be heated to an elevated temperature and to carry charged particles, and an electrical insulator disposed between the conductive wall and the thermal insulator. The thermal insulator is configured to thermally insulate the electrical insulator from the combustion volume. The electrical insulator is configured to electrically insulate the conductive wall from the thermal insulator and the combustion volume.

In one embodiment, an electrically floating conductive foil is positioned between two layers of the thermal insulator material so as to redistribute any charge that finds its way past the first thermally insulating layer.

According to an embodiment, a combustor includes a furnace wall defining a combustion chamber configured to enclose a combustion reaction, a power supply configured to output a high voltage, and a charger operatively coupled to the power supply and to the combustion chamber. The charger is configured to receive the high voltage from the power supply and to cause the combustion reaction to carry a majority charge. The furnace wall includes a conductive wall, a thermal insulator adjacent to the combustion chamber, and an electrical insulator disposed between the thermal insulator and the conductive wall. The thermal insulator is configured to thermally insulate the electrical insulator from the combustion volume. The electrical insulator is configured to electrically insulate the conductive wall from the thermal insulator and the combustion volume.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a sectional diagram of a combustor wall, according to an embodiment.

FIG. 2 is a sectional diagram of a combustor wall, according to another embodiment.

FIG. 3 is a diagram of a combustor, according to an embodiment.

FIG. 4 is a diagram of a combustor, according to another embodiment.

FIG. 5 is a flow diagram of a process for operating a combustor, according to one embodiment.

DETAILED DESCRIPTION

In the following detailed description, reference is made to the accompanying drawings, which form a part hereof. In the drawings, similar symbols typically identify similar components, unless context dictates otherwise. Other embodiments may be used and/or other changes may be made without departing from the spirit or scope of the disclosure.

FIG. 1 is a sectional diagram of a combustor wall 100, according to an embodiment. The combustor wall 100 includes a conductive wall 102 defining an exterior surface 104 configured to lie adjacent to an outer volume 106 and configured to provide tensile strength to the combustor wall 100. A thermal insulator 108 defining an interior surface 110 is configured to lie adjacent to a combustion volume 112. The combustion volume 112 is configured to be heated to an elevated temperature and to carry charged particles 114. An electrical insulator 116 is disposed between the conductive wall 102 and the thermal insulator 108. The thermal insulator 108 is configured to thermally insulate the electrical insulator 116 from the combustion volume 112. The electrical insulator 116 is configured to electrically insulate the conductive wall 102 from the thermal insulator 108 and the combustion volume 112.

The outer volume 106 adjacent to the exterior surface 104 of the conductive wall 102 can be atmospheric and/or a water jacket, for example. The conductive wall 102 can be steel or iron and can be electrically grounded. The electrical insulator 116 is contemplated to include several alternative materials. For example, in one embodiment, the electrical insulator 116 was steatite, also referred to as soapstone. Steatite has a relatively low electrical conductivity that is persistent to relatively high temperatures. Low electrical conductivity at high temperatures can be leveraged to reduce the thickness of the thermal insulating layer 108. Thermal insulating properties of the electrical insulator 116 can similarly be leveraged to reduce the thickness of the thermal insulator 108. In other embodiments, other electrical insulator materials and structures may be used. For example, some electrically insulating materials may be selected for a relatively high dielectric constant (at least at a modulation frequency of the charged particles 114), a melting point or glass transition temperature high enough to avoid degradation, and/or a coefficient of thermal expansion that is relatively well-matched to that of the material in the wall 102 and/or the thermal insulator 108. For example, the electrical insulator 116 may include one or more of polyether-ether-ketone, polyimide, silicon dioxide, silica glass, alumina, silicon, titanium dioxide, strontium titanate, barium strontium titanate, or barium titanate. More electrically conductive (poorer electrically insulating) material options (such as polyimide, polyether-ether-ketone, silicon dioxide, silica glass, or silicon) may be most appropriate for the electrical insulator 116 for embodiments using lower voltages, greater electrical insulator 116 thicknesses, and/or greater thermal insulator 108 thicknesses.

The thermal insulator 108 can be a ceramic fiber, a refractory fiber, and/or a refractory ceramic fiber. For example, the thermal insulator 108 can be a vitreous aluminosilicate fiber. For thermal insulator 108 materials that include binder materials that are relatively lower melt point or higher thermal conductivity, the thermal insulator 108 can be heat treated to remove (“burn off”) the binders. The thermal insulator 108 can additionally or alternatively include cordierite (magnesium iron aluminum cyclosilicate), Mullite (a silicate mineral including Al₂O₃ and SiO₂, as 2Al₂O₃SiO₂ or 3Al₂O₃2SiO₂.), alumina, and/or an aerogel. The thermal insulator 108 can be formed as a honeycomb material or having another structure including air gap thermally insulating features.

FIG. 2 is a sectional diagram of a combustor wall 200, according to another embodiment. The thermal insulator 108 can include quiescent air channels 202. The thermal insulator 108 can be selected to be electrically conductive at elevated temperatures. At least a portion of the thermal insulator 108 can be configured to act as an electrode at elevated temperatures.

FIG. 3 is a diagram of a combustor 300, according to an embodiment. The combustor 300 includes a furnace wall 302 defining the combustion volume 112 configured to enclose a combustion reaction 304. A power supply 306 is configured to output a high voltage. A charger 308 is operatively coupled to the power supply 306 and to the combustion volume 112 and configured to receive the high voltage from the power supply 306 and to cause the combustion reaction 304 to carry a majority charge. The furnace wall 302 includes the conductive wall 102 adjacent to an outside volume 106, the thermal insulator 108 adjacent to the combustion volume 112, and the electrical insulator 116 disposed between the thermal insulator 108 and the conductive wall 102. The conductive wall 102 can define a water jacket. The conductive wall 102 can include steel and/or iron.

As described above, the electrical insulator 116 can include steatite or another material having suitable properties. The electrical insulator 116 can be configured as a plurality of continuous planes respectively held by gravity adjacent to the conductive wall 102. Additionally or alternatively, the electrical insulator 116 can be configured as a plurality of tiles. Air gaps between adjacent tiles may provide electrical insulation and reduce the need for close fitting of the tiles. For example, the tiles may be separated from one another by up to 0.25 inch in some installations. In other installations, the tiles are installed within 0.125 inch of one another. In some installations, the tiles are installed within 0.0625 of one another.

In some embodiments, the electrical insulator 116 can include two or more layers of insulating tiles (e.g., soapstone tiles). Tiles in respective layers can be offset from one another to minimize or eliminate any single gap penetrating the entire thickness of the electrical insulator 116 (e.g., a two-layer field of electrically insulating tiles can include tiles centered on every three- or four-corner abutting location on an underlying layer of electrically insulating tiles.

The electrical insulator 116 can be adhered to the conductive wall 102 and/or to adjoining electrical insulator layers by adhesive. In an embodiment, the electrical insulator 116 can be affixed to the conductive wall 102, other layers of the electrical insulator 116, and/or to the thermal insulator 108 by a cementitious material that acts an adhesive. In another embodiment, the electrical insulator 116 can be affixed to the conductive wall 102, other layers of the electrical insulator 116, and/or to the thermal insulator 108 by an adhesive material. In another embodiment, the electrical insulator 116 can be affixed to the conductive wall 102, other layers of the electrical insulator 116, and/or to the thermal insulator 108 by nonconductive hardware. For example, alumina screws or posts (including tensile reinforced alumina screws or posts) can mechanically adjoin the electrical insulator 116 to the conductive wall 102, other layers of the electrical insulator 116, and/or to the thermal insulator 108.

The thermal insulator 108 can include a ceramic fiber, a refractory fiber, and/or a refractory ceramic fiber, according to embodiments. The thermal insulator 108 can be held adjacent to the electrical insulator 116 by gravity. Additionally or alternatively, the thermal insulator 108 can be adhered to the electrical insulator 116 by an adhesive and/or by substantially non-conducting fasteners. In an embodiment, the thermal insulator 108 can include a vitreous aluminosilicate fiber. The thermal insulator 108 can be heat treated to remove binders. The thermal insulator 108 can additionally or alternatively include cordierite, Mullite, alumina, and/or an aerogel. The thermal insulator 108 can be formed as a honeycomb or porous material.

The thermal insulator 108 can be configured, under steady-state conditions, to thermally insulate the electrical insulator 116 sufficiently to maintain at least a 700° F. difference between the combustion volume 112 and the electrical insulator 116. In some embodiments, the thermal insulator 108 may be configured to maintain a 1700° F. difference (steady-state) between the combustion volume 112 and the electrical insulator 116.

In one embodiment, the electrical insulator is configured to inhibit leakage current between the charger 308 and outer wall 102 at elevated temperatures. For example, the electrical insulator is configured to allow a maximum voltage drop across the electrical insulator 116 corresponding to 5% of the voltage between the outer wall 102 and the charger 308. Thus, if 40 kV are applied between the charger 308 and the outer wall 102, then a voltage drop of 2 kV is permitted across the electrical insulator 116.

In an embodiment, the electrical insulator 116 maintains at least 10 megaohms resistance between the combustion volume 112 and the furnace wall 302. In another embodiment, the electrical insulator 116 can maintain at least 100 megaohms of resistance to a grounded furnace wall 102. The conductive wall 102 can be held at an electrical ground such as earth ground.

The power supply 306 can be configured to output a high voltage greater than 1000V magnitude. In another embodiment, the power supply 306 can be configured to output a high voltage equal to or greater than 15 kV in magnitude. The power supply 306 can be configured to output a DC voltage and/or output an AC voltage.

The combustor 300 can be a solid fuel 310 burner. The charger 308 can be configured to output an AC high voltage to the combustion reaction 304. The combustor 300 can include a conductive grate 312 configured to act as a counter electrode to the charger 308. The conductive grate 312 can be galvanically isolated.

FIG. 4 is a diagram of a combustor 400, according to another embodiment. The combustor 300 can be a gas burner 400. The combustor 400 can include an electrically grounded fuel nozzle 402. The combustor 400 can include a second power supply voltage lead 404 configured to carry a voltage. A region 406 of the thermal insulator 108 can be operatively coupled to the second power supply voltage lead 404. The thermal insulator 108 can become electrically conductive at elevated temperatures responsive to heating by the combustion reaction 304. At least the region 406 of the thermal insulator 108 can be configured to operate as an electrode upon being heated by the combustion reaction 304. In the combustor 400, the second power supply voltage lead 404 can pass through an aperture 408 defined by the conductive wall 102.

FIG. 5 is a flow diagram of a process 500 for operating a combustor, according to one embodiment. At 502 a combustion reaction is initiated in a combustion chamber of a combustor. A wall of the combustion chamber includes an outer conductive layer, an inner thermal insulation layer, and an intermediate electrical insulation layer positioned between the outer conductive layer and the thermal insulation layer. The conductive outer layer is coupled to a power supply. A charger electrode may be positioned within the combustion chamber and is coupled to the power supply. Alternatively, a charged particle emission electrode may be positioned within the combustion chamber or may be positioned within a gas stream that enters the combustion chamber, such as a combustion air stream, a flue gas recirculation stream, or a gaseous fuel stream. Additionally or alternatively, the combustion chamber may be at least partly tribo-electrically charged, such as by contact-generated charges carried into the combustion chamber by fuel particles.

As the combustion reaction proceeds, the temperature of the gas within the combustion chamber rises until it reaches a steady-state temperature. The thermal insulation layer thermally insulates the electrical insulation layer and the conductive outer wall such that the temperature of the electrical insulation layer is significantly lower than the temperature within the combustion chamber.

At 504 a ground voltage is applied to the conductive outer layer of the wall of the combustion chamber. Alternatively, a voltage other than ground may be applied to the conductive outer layer of the wall of the combustion chamber. Typically, the conductive outer layer may be held at ground by virtue of its continuity with an external environment and/or via a grounded conductor.

At 506 a high voltage is applied to the charger within the combustion chamber. When the high voltage is applied to the charger in the combustion chamber, gases undergoing the combustion reaction are ionized such that a flame within the combustion chamber carries a majority charge. In this way, the characteristics of the combustion reaction within the combustion chamber can be controlled to have selected characteristics. In one embodiment, the high-voltage applied to the charger is between 1000V and 15,000V. Alternatively, the high-voltage can be higher than 15,000V. The voltage applied to the charger can be an AC voltage, a DC voltage, or any suitable waveform to obtain selected characteristics of the combustion reaction within the combustion chamber.

According to one embodiment, at high temperatures the thermal insulation layer becomes electrically conductive. A portion of the thermal insulation layer can be used as an electrode for further controlling characteristics of the combustion reaction within the combustion chamber. Thus, in one embodiment the process 500 comprises applying ground voltage or a third voltage to the portion of the thermal insulation layer used as an electrode. The voltage can be applied to thermal insulation layer by passing a conductor through an aperture in the conductive outer layer and the electrical insulation layer to the thermal insulation layer.

In one embodiment, the process 500 includes cooling the outer conductive layer of the wall of the combustion chamber by passing water along the outside of the conductive layer of the combustion chamber wall. In this case, a water jacket configuration contains the water as it is passed along the outer conductive layer of the wall of the combustion chamber. The water jacket is thermally coupled to the outer conductive layer of the combustion chamber wall such that the water cools the outer conductive layer of the combustion chamber wall. Similarly, the water jacket may act as at least a portion of a thermal load that is heated by the combustion reaction.

In one embodiment, a conductor is positioned adjacent a bottom portion of the combustion chamber. Therefore, in one embodiment the process 500 includes applying a voltage to the conductor near the bottom of the combustion chamber. In this case, the conductor near the bottom of the combustion chamber acts as a counter electrode to the charger. The conductor at the bottom of the combustion chamber can be connected to ground or can carry any other suitable voltage to influence the combustion reaction. Alternatively, the conductor at the bottom of the combustion chamber can be connected to a voltage through an electrically resistive material.

In one embodiment the combustor burns liquid or gaseous fuel. In this case the conductor near the bottom of the electrode can be a conductive fuel nozzle from which fuel is output into the combustion chamber. Alternatively, if the combustor burns a solid fuel, the conductor near the bottom of the combustion chamber can be a conductive grid or mesh on which the solid fuel is disposed during combustion and/or during preheating awaiting combustion.

While the steps of the process 500 have been described as occurring in a particular order, the steps of the process 500 can be performed in different orders then shown in FIG. 5 and described in the foregoing description. For example, the voltages can be applied to the conductive outer layer and the charger prior to initiation of the combustion reaction, or simultaneous with the initiation of the combustion reaction. Those skilled in the art will understand, in light of the present disclosure, that many other process steps and orders of performing the process steps are possible in accordance with principles of the present disclosure. All such other orders and process steps fall within the scope of the present disclosure.

While various aspects and embodiments have been disclosed herein, other aspects and embodiments are contemplated. The various aspects and embodiments disclosed herein are for purposes of illustration and are not intended to be limiting, with the true scope and spirit being indicated by the following claims. 

What is claimed is:
 1. A combustor, comprising: a furnace wall defining a combustion chamber configured to enclose a combustion reaction; a power supply configured to output a high voltage; and a charger operatively coupled to the power supply and to the combustion chamber and configured to receive the high voltage from the power supply and to cause the combustion reaction to carry a charge; wherein the furnace wall includes a conductive wall adjacent to an outside volume, a thermal insulator adjacent to the combustion chamber, and an electrical insulator disposed between the thermal insulator and the conductive wall.
 2. The combustor of claim 1, wherein the thermal insulator is configured to thermally insulate the electrical insulator from the combustion volume; and wherein the electrical insulator is configured to electrically insulate the conductive wall from the thermal insulator and the combustion volume.
 3. The combustor of claim 1, wherein the conductive wall defines a water jacket.
 4. The combustor of claim 1, wherein the outside volume is accessible to a human during normal operation of the combustor.
 5. The combustor of claim 1, wherein the electrical insulator includes steatite.
 6. The combustor of claim 1, wherein the electrical insulator is configured as a plurality of continuous planes respectively held by gravity adjacent to the conductive wall.
 7. The combustor of claim 1, wherein the electrical insulator is configured as a plurality of tiles.
 8. The combustor of claim 7, wherein the electrical insulator is configured as a plurality of tiles with air gaps therebetween.
 9. The combustor of claim 1, wherein the electrical insulator includes a vacuum.
 10. The combustor of claim 1, wherein the electrical insulator includes air.
 11. The combustor of claim 1, wherein the thermal insulator includes a ceramic fiber, a refractory fiber, or a refractory ceramic fiber.
 12. The combustor of claim 1, wherein the thermal insulator includes a vitreous aluminosilicate fiber.
 13. The combustor of claim 1, wherein the thermal insulator includes cordierite.
 14. The combustor of claim 1, wherein the thermal insulator includes Mullite.
 15. The combustor of claim 1, wherein the thermal insulator includes alumina.
 16. The combustor of claim 1, wherein the thermal insulator includes an aerogel.
 17. The combustor of claim 1, wherein the thermal insulator is formed as a honeycomb material.
 18. The combustor of claim 1, wherein the thermal insulator includes quiescent air channels.
 19. The combustor of claim 1, wherein the thermal insulator is configured to insulate the electrical insulator sufficiently to maintain at least 10 megaohms per square.
 20. The combustor of claim 1, wherein the thermal insulator is configured to insulate the electrical insulator sufficiently to maintain at least 20 megaohms of resistance to ground.
 21. The combustor of claim 1, wherein the conductive wall is in electrical continuity with electrical ground.
 22. The combustor of claim 1, wherein the power supply is configured to output a high voltage greater than 1000V magnitude.
 23. The combustor of claim 22, wherein the power supply is configured to output a high voltage equal to or greater than 15 kV magnitude.
 24. The combustor of claim 1, wherein the thermal insulator includes: a first thermal insulator layer; a second thermal insulator layer; and an electrically floating electrical conductor positioned between the first and second thermal insulator layers.
 25. The combustor of claim 1, wherein the combustor is a solid fuel burner.
 26. The combustor of claim 1, wherein the combustor is a gas burner.
 27. The combustor of claim 1, further comprising: a second power supply voltage lead configured to carry a voltage; and a region of the thermal insulator operatively coupled to second power supply voltage lead.
 28. The combustor of claim 27, wherein the thermal insulator becomes electrically conductive at elevated temperatures responsive to heating by the combustion reaction; and wherein at least the region of the thermal insulator is configured to operate as an electrode upon being heated by the combustion reaction.
 29. The combustor of claim 27, wherein the second power supply voltage lead passes through an aperture defined by the conductive wall.
 30. A method comprising: supporting a combustion reaction in a combustion chamber; maintaining a first voltage on a conductive wall of the combustion chamber; electrically insulating the conductive wall from the combustion reaction with an electrical insulation layer; thermally insulating the electrical insulation layer from the combustion reaction with a thermal insulation layer separate from the electrical insulation layer; and applying a second high voltage to the combustion reaction.
 31. The method of claim 30, wherein maintaining the first voltage includes maintaining electrical continuity with electrical ground.
 32. The method of claim 30, wherein applying the second high voltage includes applying between 1000V and 15,000V to the combustion reaction.
 33. The method of claim 30, further comprising applying a third voltage to the thermal insulation layer.
 34. The method of claim 33, wherein applying the third voltage to the thermal insulator includes applying the third voltage to a conductor that passes through an aperture in the conductive wall and the electrical insulation layer.
 35. The method of claim 33, wherein the thermal insulator becomes electrically conductive at a temperature characteristic of the combustion reaction; and wherein applying the third voltage to the thermal insulator includes causing a portion of the thermal insulator to operate as an electrode.
 36. The method of claim 30, further comprising cooling the conductive wall by passing water through a water jacket thermally coupled to the conductive wall.
 37. The method of claim of claim 30, further comprising: passing a fuel for the combustion reaction into the combustion chamber through a conductive grate; and applying a third voltage to the conductive grate.
 38. The method of claim 30, wherein the thermal insulation layer includes quiescent air channels.
 39. The method claim 30, wherein the thermal insulation layer includes a vitreous aluminosilicate fiber.
 40. The method of claim 30, wherein the thermal insulator layer includes cordierite.
 41. The method of claim 30, wherein the electrical insulator layer comprises a plurality of steatite tiles separated from each other by air gaps.
 42. The method of claim 30, wherein applying a second high voltage to the combustion reaction further comprises: passing a gas stream into the combustion chamber; operating a charger to output charged particles to the gas stream; and electrically energizing the combustion reaction with the charged particles from the charger. 